Boilerplate

Boilerplate is a tool for generating files and folders ("boilerplate") from a set of templates.

Example use cases:

Scaffold out a new repo, folder, or file.
Fill in boilerplate sections in your code files, such as including a legal disclaimer or license at the top of each source file, or updating a version number in a file after each build.
Embed code snippets from actual source files in documentation. Most READMEs have code copy/pasted into them and that code often has syntax errors or goes out of date. Now you can keep those code examples in normal source files which are built & tested, and embed parts of those files dynamically in your docs.

See Introducing Boilerplate for a quick introduction.

Example: creating a new template

Create a folder called website-boilerplate and put a file called boilerplate.yml in it:

variables:
  - name: Title

  - name: WelcomeText
    description: Enter the welcome text for the website

  - name: ShowLogo
    description: Should the website show the logo?
    type: bool
    default: true

This file defines 3 variables: Title, WelcomeText, and ShowLogo. When you run Boilerplate, it will prompt the user for each one.

Next, create an index.html in the website-boilerplate folder that uses these variables using Go Template syntax:

<html>
  <head>
    <title>{{.Title}}</title>
  </head>
  <body>
    <h1>{{.WelcomeText}}</h1>
    {{if .ShowLogo}}<img src="logo.png">{{end}}
  </body>
</html>

Copy an image into the website-boilerplate folder and call it logo.png.

Finally, run boilerplate, setting the --template-url to website-boilerplate and --output-folder to the path where you want the generated code to go:

boilerplate --template-url /home/ubuntu/website-boilerplate --output-folder /home/ubuntu/website-output

Title

  Enter a value [type: string]: Boilerplate Example

WelcomeText
  Enter the welcome text for the website

  Enter a value [type: string]: Welcome!

ShowLogo
  Should the website show the logo?

  Enter a [type: bool]: true

Generating /home/ubuntu/website-output/index.html
Copying /home/ubuntu/website-output/logo.png

Boilerplate copies any files from the --template-url into the --output-folder, passing them through the Go Template engine along the way. After running the command above, the website-output folder will contain a logo.png (unchanged from the original) and an index.html with the following contents:

<html>
  <head>
    <title>Boilerplate</title>
  </head>
  <body>
    <h1>Welcome!</h1>
    <img src="logo.png">
  </body>
</html>

You can also run Boilerplate non-interactively, which is great for automation:

boilerplate \
  --template-url /home/ubuntu/website-boilerplate \
  --output-folder /home/ubuntu/website-output \
  --non-interactive \
  --var Title="Boilerplate Example" \
  --var WelcomeText="Welcome!" \
  --var ShowLogo="true"

Generating /home/ubuntu/website-output/index.html
Copying /home/ubuntu/website-output/logo.png

Of course, Boilerplate can be used to generate any type of project, and not just HTML, so check out the examples folder for more examples and the Working with Boilerplate section for full documentation.

Install

Download the latest binary for your OS here.

You can find older versions on the Releases Page.

Features

Interactive mode: Boilerplate interactively prompts the user for a set of variables defined in a boilerplate.yml file and makes those variables available to your project templates during copying.
Non-interactive mode: Variables can also be set non-interactively, via command-line options, so that Boilerplate can be used in automated settings (e.g. during automated tests).
Flexible templating: Boilerplate uses Go Template for templating, which gives you the ability to do formatting, conditionals, loops, and call out to Go functions. It also includes helpers for common tasks such as loading the contents of another file.
Variable types: Boilerplate variables support types, so you have first-class support for strings, ints, bools,
Validations: Boilerplate provides a set of validations for a given variable that user input must satisfy.
Variable presentation order: Boilerplate allows you to define the relative presentation order of a set of variables. lists, maps, and enums.
Scripting: Need more power than static templates and variables? Boilerplate includes several hooks that allow you to run arbitrary scripts.
Cross-platform: Boilerplate is easy to install (it's a standalone binary) and works on all major platforms (Mac, Linux, Windows).

Working with boilerplate

When you run Boilerplate, it performs the following steps:

Read the boilerplate.yml file in the folder specified by the --template-url option to find all defined varaibles.
Gather values for the variables from any --var and --var-file options that were passed in and prompting the user for the rest (unless the --non-interactive flag is specified).
Copy each file from --template-url to --output-folder, running each non-binary file through the Go Template engine with the map of variables as the data structure.

Learn more about boilerplate in the following sections:

Boilerplate command line options
The boilerplate.yml file
Variables
Dependencies
Hooks
Skip Files
Templates
Validations
Variable Ordering
Alternative Template Engines (EXPERIMENTAL)
Template helpers
Deprecated helpers
Partials

Boilerplate command line options

The boilerplate binary supports the following options:

--template-url URL (required): Generate the project from the templates in URL. This can be a local path, or a go-getter compatible URL for remote templates (e.g., git@github.com:gruntwork-io/boilerplate.git//examples/for-learning-and-testing/include?ref=main).
--output-folder (required): Create the output files and folders in FOLDER.
--non-interactive (optional): Do not prompt for input variables. All variables must be set via --var and --var-file options instead.
--var NAME=VALUE (optional): Use NAME=VALUE to set variable NAME to VALUE. May be specified more than once.
--var-file FILE (optional): Load variable values from the YAML file FILE. May be specified more than once.
--missing-key-action ACTION (optional): What to do if a template looks up a variable that is not defined. Must be one of: invalid (render the text ""), zero (render the zero value for the variable), or error (return an error and exit immediately). Default: error.
--missing-config-action ACTION (optional): What to do if a template folder does not have a boilerplate.yml file. Must be one of: exit (return an error and exit immediately) or ignore (log a warning and process the template folder without any variables). Default: exit.
--disable-hooks: If this flag is set, no hooks will execute.
--disable-shell: If this flag is set, no shell helpers will execute. They will instead return the text "replace-me".
--disable-dependency-prompt (optional): Do not prompt for confirmation to include dependencies. Has the same effect as --non-interactive, without disabling variable prompts. Default: false.
--help: Show the help text and exit.
--version: Show the version and exit.

Some examples:

Generate a project in ~/output from the templates in ~/templates:

boilerplate --template-url ~/templates --output-folder ~/output

Generate a project in ~/output from the templates in ~/templates, using variables passed in via the command line:

boilerplate --template-url ~/templates --output-folder ~/output --var "Title=Boilerplate" --var "ShowLogo=false"

Generate a project in ~/output from the templates in ~/templates, using variables read from a file:

boilerplate --template-url ~/templates --output-folder ~/output --var-file vars.yml

Generate a project in ~/output from the templates in this repo's include example dir, using variables read from a file:

boilerplate --template-url "git@github.com:gruntwork-io/boilerplate.git//examples/for-learning-and-testing/include?ref=main" --output-folder ~/output --var-file vars.yml

The boilerplate.yml file

The boilerplate.yml file is used to configure boilerplate. The file is optional. If you don't specify it, you can still use Go templating in your templates so long as you specify the --missing-config-action ignore option, but no variables or dependencies will be available.

boilerplate.yml uses the following syntax:

required_version: <VERSION_CONSTRAINT>

variables:
  - name: <NAME>
    description: <DESCRIPTION>
    type: <TYPE>
    options:
      - <CHOICE>
      - <CHOICE>
    default: <DEFAULT>
    reference: <NAME>

dependencies:
  - name: <DEPENDENCY_NAME>
    template-url: <FOLDER>
    output-folder: <FOLDER>
    skip: <CONDITION>
    dont-inherit-variables: <BOOLEAN>
    for_each: <LIST>
    for_each_reference: <NAME>
    variables:
      - name: <NAME>
        description: <DESCRIPTION>
        type: <TYPE>
        default: <DEFAULT>

hooks:
  before:
    - command: <CMD>
      args:
        - <ARG>
      env:
        <KEY>: <VALUE>
      skip: <CONDITION>
  after:
    - command: <CMD>
      args:
        - <ARG>
      env:
        <KEY>: <VALUE>
      skip: <CONDITION>

partials:
  - <GLOB>
  - <GLOB>

Here's an example:

variables:
  - name: Description
    description: Enter the description of this template

  - name: Version
    description: Enter the version number that will be used by the docs dependency

  - name: Title
    description: Enter the title for the dependencies example

  - name: WelcomeText
    description: Enter the welcome text used by the website dependency

  - name: ShowLogo
    description: Should the webiste show the logo (true or false)?
    type: bool
    default: true

dependencies:
  - name: docs
    template-url: ../docs
    output-folder: ./docs
    variables:
      - name: Title
        description: Enter the title of the docs page

  - name: website
    template-url: ../website
    output-folder: ./website
    variables:
      - name: Title
        description: Enter the title of the website

skip_files:
  - path: .ignore-me
  - path: subfolder/README.md
    if: {{ not .ShowLogo }}

engines:
  - path: subfolder/foo.json.jsonnet
    template_engine: jsonnet

partials:
  - ../html/*.html
  - ../css/*.css
  - ../other/somefile.html

Required Version: A version constraint string in the same format as Terraform that can be used to specify what versions of Boilerplate are supported by the config.

Variables: A list of objects (i.e. dictionaries) that define variables. Each variable may contain the following keys:

name (Required): The name of the variable.
description (Optional): The description of the variable. boilerplate will show this description to the user when prompting them for a value.
type (Optional): The type of the variable. Must be one of: string, int, float, bool, map, list, enum. If unspecified, the default is string.
options (Optional): If the type is enum, you can specify a list of valid options. Each option must be a string.
default (Optional): A default value for this variable. The user can just hit ENTER at the command line to use the default value, if one is provided. If running Boilerplate with the --non-interactive flag, the default is used for this value if no value is provided via the --var or --var-file options.
reference (Optional): The name of another variable whose value should be used for this one.

See the Variables section for more info.

Dependencies: A list of objects (i.e. dictionaries) that define other boilerplate templates to execute before executing the current one. Each dependency may contain the following keys:

name (Required): A unique name for the dependency.
template-url (Required): Run boilerplate on the templates in this folder. This path is relative to the current template.
output-folder (Required): Create the output files and folders in this folder. This path is relative to the output folder of the current template.
skip (Optional): Skip this dependency if this condition, which can use Go templating syntax and boilerplate variables, evaluates to the string true. This is useful to conditionally enable or disable dependencies.
dont-inherit-variables (Optional): By default, any variables already set as part of the current boilerplate.yml template will be reused in the dependency, so that the user is not prompted multiple times for the same variable. If you set this option to false, then the variables from the parent template will not be reused.
variables: If a dependency contains a variable of the same name as a variable in the root boilerplate.yml file, but you want the dependency to get a different value for the variable, you can specify overrides here. Note that these variables will not influence the boilerplate prompts.
var_files: If you want to set the variables for the dependency based on a var file, you can provide a list of var file paths to include. The path is assumed to be relative to the current boilerplate.yml, but it is recommended to use the templateFolder helper function to be explicit. Note that the order of preference for variables are (top most have highest precedence - aka override all):
- Top level variables set on the CLI.
- Var files set on the dependency.
- Defaults set on dependency variables (the variables field of the dependency).
- Defaults set on root variables.
- Defaults set within the dependency boilerplate config.
for_each: If you set this to a list of values, boilerplate will loop over each value, and render this dependency once for each value. This allows you to dynamically render a dependency multiple times based on user input. The current value in the loop will be available as the variable __each__, available to both your Go templating and in other dependencies params: e.g., you could reference {{ .__each__ }} in output-folder to render to each iteration to a different folder.
for_each_reference: The name of another variable whose value should be used as the for_each value.

See the Dependencies section for more info.

Partials: Use partials to include reusable templates. Partials are defined using a list of glob patterns.

Globs are matched using the Go filepath.Glob function
In the event of a template name collision (e.g. multiple templates are defined with the same name), the last one wins.

See the Partials section for more info.

Skip Files: Use skip_files to specify files in the template folder that should not be rendered. The path field is the relative path from the template folder root (where the boilerplate.yml file is defined) of the file that should be excluded. You can conditionally skip the file using the if field, which should either be a YAML boolean value (true or false), or Go templating syntax (which can use the boilerplate variables) that evaluates to the string values "true" or "false".

See the Skip Files section for more info.

Engines: Use engines to specify files in the template folder that should be rendered with an alternative templating engine. The path field is the relative path from the template folder root (where the boilerplate.yml file is defined) of the file that should use the alternative template engine.

See the Alternative Template Engines (EXPERIMENTAL) section for more info.

Hooks: Boilerplate provides hooks to execute arbitrary shell commands. There are two types of hooks:

before (Optional): A list of scripts to execute before any template rendering has started.
after (Optional): A list of scripts to execute after all template rendering has completed.

See the Hooks section for more info.

Variables

You must provide a value for every variable defined in boilerplate.yml, or project generation will fail. There are five ways to provide a value for a variable:

--var option(s) you pass in when calling boilerplate. Example: boilerplate --var Title=Boilerplate --var ShowLogo=false. To specify a complex type like a map or a list on the command-line, use YAML syntax (preferably the shorthand variety to keep it a one-liner). For example --var foo='{key: "value"}' --var bar='["a", "b", "c"]'. If you want to specify the value of a variable for a specific dependency, use the <DEPENDENCY_NAME>.<VARIABLE_NAME> syntax. For example: boilerplate --var Description='Welcome to my home page!' --var about.Description='About Us' --var ShowLogo=false.
--var-file option(s) you pass in when calling boilerplate. Example: boilerplate --var-file vars.yml. The vars file must be a simple YAML file that defines key, value pairs, where the key is the name of a variable (or <DEPENDENCY_NAME>.<VARIABLE_NAME> for a variable in a dependency) and the value is the value to set for that variable. Example:
```
Title: Boilerplate
ShowLogo: false
Description: Welcome to my home page!
about.Description: Welcome to my home page!
ExampleOfAMap:
  key1: value1
  key2: value2
ExampleOfAList:
  - value1
  - value2
```
Manual input. If no value is specified via the --var or --var-file flags, Boilerplate will interactively prompt the user to provide a value. Note that the --non-interactive flag disables this functionality.
Defaults defined in boilerplate.yml. The final fallback is the optional default that you can include as part of the variable definition in boilerplate.yml.
An environment variable with the name BOILERPLATE_<VARIABLE_NAME>. For example, if you have a variable called Title, you can set the value of this variable by setting the environment variable BOILERPLATE_Title (note the case sensitivity). This is useful for automation and CI/CD pipelines.

Note that variables can reference other variables using Go templating syntax:

variables:
  - name: Foo
    default: foo

  - name: Bar
    default: "{{ .Foo }}-bar"

If you rendered {{ .Bar }} with the variables above, you would get foo-bar. Note that this will always return a string. If you want to reference another variable of a non-string type (e.g. a list), use the reference keyword:

variables:
  - name: Foo
    type: list
    default:
      - 1
      - 2
      - 3

  - name: Bar
    type: list
    reference: Foo

In the example above, the Bar variable will be set to the same (list) value as Foo.

Dependencies

Specifying dependencies within your boilerplate.yml files allows you to chain multiple boilerplate templates together. This allows you to create more complicated projects from simpler pieces.

Note the following:

Recursive dependencies: Dependencies can include other dependencies. For example, the boilerplate.yml in folder A can include folder B in its dependencies list, the boilerplate.yml in folder B can include folder C in its dependencies list, and so on.
Inheriting variables: You can define all your common variables in the root boilerplate.yml and any variables with the same name in the boilerplate.yml files of your dependencies list will reuse those variables instead of prompting the user for the same value again.
Variable conflicts: Sometimes, two dependencies use a variable of the same name, but you want them to have different values. To handle this use case, you can define custom variable blocks for each dependency and boilerplate will prompt you for each of those variables separately from the root ones. You can also use the <DEPENDENCY_NAME>.<VARIABLE_NAME> syntax as the name of the variable with the -var flag and inside of a var file to provide a value for a variable in a dependency.
Interpolation: You may use interpolation in the template-url and output-folder parameters of your dependencies. This allows you to use specify the paths to your template and output folders dynamically.

Conditional dependencies: You can enable or disable a dependency using the skip parameter, which supports Go templating syntax and boilerplate variables. If the skip parameter evaluates to the string true, the dependency will be skipped; otherwise, it will be rendered. Example:

variables:
  - name: Foo
    type: bool

  - name: Bar
    type: bool

dependencies:
  - name: conditional-dependency-example
    template-url: ../foo
    output-folder: foo
    # Skip this dependency if both .Foo and .Bar are set to true
    skip: "{{ and .Foo .Bar }}"

Looping over dependencies: You can render a dependency multiple times, dynamically, based on user input, via the for_each or for_each_reference parameter. Example:

variables:
  - name: environments
    description: The environments to deploy into (e.g., dev, stage, prod)
    type: list
    default:
      - dev
      - stage
      - prod

dependencies:
  - name: loop-dependency-example
    template-url: ../terraform
    # Render this dependency once for each environment the user specifies
    for_each_reference: environments
    # Render the dependency to an output folder that includes the environment name
    output-folder: "live/{{ .__each__ }}"
    variables:
      - name: ServerName
        description: The name to use for the EC2 instance (for its Name tag)
        type: string
        # Use the environment name in the server name
        default: "example-{{ .__each__ }}"

Confirming dependency includes: By default in interactive mode, the user must confirm to include each dependency. If --non-interactive is set, dependencies will be included automatically, so long as skip is false. If you'd like to keep interactive mode enabled, but disable dependency confirmation, set --disable-dependency-prompt.

Hooks

You can specify hooks in boilerplate.yml to tell Boilerplate to execute arbitrary shell commands.

Note the following:

The before hook allows you to run scripts before Boilerplate has started rendering.
The after hook allows you to run scripts after Boilerplate has finished rendering.
Each hook consists of a command to execute (required), a list of args to pass to that command (optional), a map of environment variables in env to set for the command (optional), and the working directory dir in which to run the command (optional). Example:
```
before:
  - command: echo
    args:
      - Hello
      - World
    env:
      FOO: BAR
    dir: "/foo/bar"
```
You can use Go templating syntax in command, args, env, and dir. For example, you can pass Boilerplate variables to your scripts as follows:
```
before:
  - command: foo.sh
    args:
      - {{ .SomeVariable }}
      - {{ .AnotherVariable }}
```
By default, Boilerplate runs your command with the working directory set to the --template-url option. You can override this with the dir parameter. For example, here is how you can set it to a sub-folder of the output folder:
```
after:
  - command: some-command
    dir: "{{ outputFolder }}/foo/bar"
```
skip (Optional): Skip this hook if this condition, which can use Go templating syntax and boilerplate variables, evaluates to the string true. This is useful to conditionally enable or disable dependencies.
For an alternative way to execute commands, see the shell helper in template helpers.

Skip Files

You can specify files that should be excluded from the rendered output using the skip_files section in boilerplate.yml. This is most useful when you have templates that need to conditionally exclude files from the rendered folder list.

The skip_files section is a list of objects with the fields path, not_path, and if, where one of path or not_path is required. When path is set, all files that match the path attribute will be skipped, while when not_path is set, all files that DO NOT match the not_path attribute are skipped (in other words, only paths that match not_path are kept).

if can be used to conditionally skip a file from the template folder, and it defaults to true. That is, when if is omitted, the file at the path is always excluded from the output. Note that path and not_path are always the relative path from the template root.

All three attributes (path, not_path, and if) support Go templating syntax with access to boilerplate variables and template helpers.

Consider the following boilerplate template folder:

.
├── boilerplate.yml
├── BOILERPLATE_README.md
└── docs
    ├── README_WITH_ENCRYPTION.md
    └── README_WITHOUT_ENCRYPTION.md

Suppose that you wanted to conditionally select which README to render based on some variable. You can use skip_files to implement this logic:

variables:
  - name: UseEncryption
    type: bool

skip_files:
  - path: "BOILERPLATE_README.md"
  - path: "docs/README_WITH_ENCRYPTION.md"
    if: "{{ not .UseEncryption }}"
  - path: "docs/README_WITHOUT_ENCRYPTION.md"
    if: "{{ .UseEncryption }}"
  - not_path: "docs/**/*"
    if: "{{ .DocsOnly }}"

This will:

Always skip rendering BOILERPLATE_README.md.
Skip rendering docs/README_WITHOUT_ENCRYPTION.md if UseEncryption is set to true.
Skip rendering docs/README_WITH_ENCRYPTION.md if UseEncryption is set to false.
If DocsOnly is set to true, only render the docs folder.

For a more concise specification, you can use glob syntax in the path to match multiple paths in one entry:

skip_files:
  - path: "docs/**/*"

Templates

Boilerplate puts all the variables into a Go map where the key is the name of the variable and the value is what the user provided. It then starts copying files from the --template-url into the --output-folder, passing each non-binary file through the Go Template engine, with the variable map as a data structure.

For example, if you had a variable called Title in your boilerplate.yml file, then you could access that variable in any of your templates using the syntax {{.Title}}. You can also use Go template syntax to do if-statements, for loops, and use the provided template helpers.

You can even use Go template syntax and boilerplate variables in the names of your files and folders. For example, if you were using boilerplate to generate a Java project, your template folder could contain the path com/{{.PackageName}}/MyFactory.java. If you run boilerplate against this template folder and enter "gruntwork" as the PackageName, you'd end up with the file com/gruntwork/MyFactory.java.

Validations

Boilerplate allows you to specify a set of validations when defining a variable. When a user is prompted for a variable that has validations defined, their input must pass all defined validations. If the user's input does not pass all validations, they'll be presented with real-time feedback on exactly which rules their submission is failing. Once a user's submission passes all defined validations, Boilerplate will accept their submitted value.

Here's an example prompt for a variable with validations that shows how invalid submissions are handled:

Here's an example demonstating how to specify validations when defining your variables:

variables:
  - name: CompanyName
    description: Enter the name of your organization.
    default: ""
    type: string
    validations:
      - required
      - length-5-22
      - alphanumeric

This boilerplate.yml snippet defines a variable, CompanyName which:

Must be supplied by the user. No empty or nil values will be accepted.
Must have a length between 5 and 22 characters
Must contain only alphanumeric characters (no special characters)

Currently supported validations

Boilerplate uses the go-ozzo/ozzo-validation library. The following validations are currently supported:

"required" - field cannot be empty
"length-{min-int}-{max-int}" - field must be between ${min-int} and ${max-int} characters in length
"url" - field must be a valid URL
"email" - field must be a valid email address
"alpha" - field must contain English letters only
"digit" - field must contain digits only
"countrycode2" - field must be an ISO3166 Alpha 2 Country code
"semver" - field must be a valid semantic version

Variable Ordering

Boilerplate allows you to define the relative order in which a set of variables should be presented to the user when prompting for human input.

Here's an example demonstrating how to define the relative order of a set of variables:

variables:
  - name: WebsiteURL
    order: 0
    description: Enter the URL to your homepage
 - name: ImagePath:
   order: 1
   description: Enter the full filepath to your logo image
 - name: ProfileName
   order: 2
   description: Enter the display name for your user

Alternative Template Engines (EXPERIMENTAL)

Boilerplate has experimental support for the following alternative template engines:

jsonnet

To specify an alternative template engine, you can use the engines directive to provide a path glob that matches the files that should be fed through the alternative engine. For example, the following boilerplate configuration makes it so that any file with the .jsonnet extension will be fed through the jsonnet template engine:

engines:
  - path: "**/*.jsonnet"
    template_engine: jsonnet

Note that alternative template engines are currently only supported for processing individual files, and can not be used for parsing boilerplate directives in the config file or directory names.

See below for more information on each of the template engines supported:

IMPORTANT: Support for template helpers are limited to the go templating engine at this time. Some limited functions may be available depending on the template engine. See the information for the templating engine to know which functions are supported.

Jsonnet

Jsonnet is a data template engine optimized for generating json data. Unlike go templating, jsonnet has many features that make it more friendly to write such as:

When boilerplate processes jsonnet templates, the variables are passed through as a Top Level Argument under the name boilerplateVars. This means that every jsonnet template must be defined in a way to handle the TLA argument. For example:

function(boilerplateVars) {
  person: {
    name: boilerplateVars.Name,
  },
}

Boilerplate will also make available the following helpers as external variables:

templateFolder: Set to the value of the template working dir. This is the same as what the templateFolder boilerplate helper function returns.
outputFolder: Set to the value of the output folder where the templates are rendered. This is the same as what the outputFolder boilerplate helper function returns.

While the jsonnet template engine does not support the boilerplate helper functions, it does have access to the Jsonnet standard library. You can also import any libsonnet library in your jsonnet template, including those installed with jsonnet-bundlery.

Note that to ensure you can have editor assistance while modifying jsonnet files, the jsonnet template engine in boilerplate will strip the extension suffix .jsonnet from the output file path. E.g., if your template folder contained:

.
├── boilerplate.yml
└── data.json.jsonnet

The output folder will be:

.
└── data.json

Template helpers

Your templates have access to all the standard functionality in Go Template, including conditionals, loops, and functions.

Additionally, boilerplate ships with sprig (version 3.2.1), the standard library of template functions. You can view all the functions available in sprig here. Note that there are some differences for some functions due to backwards compatibility. Take a look at Deprecated helpers.

Boilerplate also includes several custom helpers that you can access that enhance the functionality of sprig:

snippet <PATH> [NAME]: Returns the contents of the file at PATH as a string. If you specify the second argument, NAME, only the contents of the snippet with that name will be returned. A snippet is any text in the file surrounded by a line on each side of the format "boilerplate-snippet: NAME" (typically using the comment syntax for the language). For example, here is how you could define a snippet named "foo" in a Java file:
```
String str = "this is not part of the snippet";

// boilerplate-snippet: foo
String str2 = "this is part of the snippet";
return str2;
// boilerplate-snippet: foo
```
include <PATH> <VARIABLES>: Returns the contents of the file at PATH after rendering it through the templating engine with the provided variables, as a string (unlike snippet, which returns the contents of the file verbatim). Use . to pass the current variables to the included template. E.g:
```
{{ include "../source-template.snippet" . }}
```
replaceOne OLD NEW: Replace the first occurrence of OLD with NEW. This is a literal replace, not regex.
replaceAll OLD NEW: Replace all occurrences of OLD with NEW. This is a literal replace, not regex.
roundInt FLOAT: Round FLOAT to the nearest integer. E.g. 1.5 becomes 2.
ceilInt FLOAT: Round up FLOAT to the nearest integer. E.g. 1.5 becomes 2.
floorInt FLOAT: Round down FLOAT to the nearest integer. E.g. 1.5 becomes 1.
dasherize STRING: Convert STRING to a lower case string separated by dashes. E.g. "foo Bar baz" becomes "foo-bar-baz".
camelCaseLower STRING: Convert STRING to a camel case string where the first letter is lower case. E.g. "foo Bar baz" becomes "fooBarBaz".
plus NUM NUM: Add the two numbers. Unlike add in sprig, this supports float.
minus NUM NUM: Subtract the two numbers. Unlike sub in sprig, this supports float.
times NUM NUM: Multiply the two numbers. Unlike mul in sprig, this supports float.
divide NUM NUM: Divide the two numbers. Unlike div in sprig, this supports float.
numRange START END INCREMENT: Generate a slice from START to END, incrementing by INCREMENT. This provides a simple way to do a for-loop over a range of numbers.
keysSorted MAP: Return a slice that contains all the keys in the given MAP in alphanumeric sorted order. Use the built-in Go template helper .index to look up these keys in the map.
shell CMD ARGS...: Execute the given shell command, passing it the given args, and render whatever that command prints to stdout. The working directory for the command will be set to the directory of the template being rendered, so you can use paths relative to the file from which you are calling the shell helper. Any argument you pass of the form ENV:KEY=VALUE will be set as an environment variable for the command rather than an argument. For another way to execute commands, see hooks.
templateFolder: Return the value of the template working dir. This is the value of the --template-url command-line option if local template, or the download dir if remote template. Useful for building relative paths.
outputFolder: Return the value of the --output-folder command-line option. Useful for building relative paths.
envWithDefault NAME DEFAULT: Render the value of environment variable NAME. If that environment variable is empty or not defined, render DEFAULT instead.
pathExists PATH: Returns true if the given path exists on the file system.
templateIsDefined NAME: Returns a boolean indicating if template called NAME is known. Use this to conditionally include one boilerplate template with another. Most often useful along with partials.
toYaml: Encodes an input variable as a YAML string. Similar to the toJson function in sprig.

Deprecated helpers

These helpers are deprecated. They are currently available for backwards compatibility, but may be removed in future versions. Please use the alternative supported forms listed in the description.

downcase STRING: Same functionality as lower in sprig.
upcase STRING: Same functionality as upper in sprig.
capitalize STRING: Same functionality as title in sprig.
snakeCase STRING: Same functionality as snakecase in sprig.
camelCase STRING: Same functionality as camelcase in sprig.

The following functions overlap with sprig, but have different functionality. There is an equivalent function listed above under a different name. These point to the boilerplate implementations for backwards compatibility. Please migrate to using the new naming scheme, as they will be updated to use the sprig versions in future versions of boilerplate.

round: In boilerplate, round returns the integer form as opposed to float. E.g {{ round 123.5555 }} will return 124. The following supported alternative functions are available:
- roundFloat: The sprig version of round, which supports arbitrary decimal rounding. E.g {{ round 123.5555 3 }} returns 123.556. Note that {{ round 123.5555 0 }} returns 124.0.
- roundInt: Another name for the boilerplate version of round. Use this if you would like to keep old behavior.
ceil and floor: In boilerplate, ceil and floor return integer forms as opposed to floats. E.g {{ ceil 1.1 }} returns 2, as opposed to 2.0 in the sprig version. The following supported alternative functions are available:
- ceilFloat and floorFloat: The sprig version of ceil and floor.
- ceilInt and floorInt: Another name for the boilerplate version ceil and floor. Use this if you would like to keep old behavior.
env: In boilerplate, env supports returning a default value if the environment variable is not defined. The following supported alternative functions are available:
- readEnv: The sprig version of env. This always returns empty string if the environment variable is undefined.
- envWithDefault: Another name for the boilerplate version of env. Use this if you would like to keep old behavior.
keys: In boilerplate, keys returns the keys of the map in sorted order. The following supported alternative functions are available:
- keysUnordered: The sprig version of keys. This returns the list of keys in no particular order, and there is no guarantee that the order of the returned list is consistent.
- keysSorted: Another name for the boilerplate version of keys. Use this if you would like to keep old behavior.
replace: In boilerplate, replace only replaces the first occurrence in the string, as opposed to all occurrences as in sprig. The following supported alternative functions are available:
- replaceAll: The sprig version of replace.
- replaceOne: Another name for the boilerplate version of replace. Use this if you would like to keep old behavior.
slice: In boilerplate, slice returns a list of numbers in the provided range. E.g {{ slice 1 5 1 }} returns the list [1, 2, 3, 4]. The following supported alternative functions are available:
- sliceList: The sprig version of slice, which returns the slice of the given list. E.g {{ slice list n m }} returns list[n:m].
- numRange: Another name for the boilerplate version of slice. Use this if you would like to keep old behavior.
trimPrefix and trimSuffix: In boilerplate, trimPrefix and trimSuffix takes the base string first. E.g {{ trimPrefix hello-world hello }} returns -world. The following supported alternative functions are available:
- trimPrefixSprig and trimSuffixSprig: The sprig version of trimPrefix and trimSuffix. Unlike the boilerplate version, this takes the trim text first so that you can pipeline the trimming. E.g {{ "hello-world" | trimPrefix "hello" }} returns {{ -world }}.
- trimPrefixBoilerplate and trimSuffixBoilerplate: Another name for the boilerplate versions of trimPrefix and trimSuffix. Use this if you would like to keep old behavior.

Partials

Partials help to keep templates DRY. Using partials, you can define templates in external files, and then use those templates over and over again in other templates. Partials are common among templating engines, such as in Hugo.

Let's start with a simple example. In an HTML document, we might want to have a common set of meta tags to reuse throughout our site:

<html>
  <head>
    <meta charset="UTF-8">
    <meta name="author" content="Gruntwork">
  </head>
  <body>
    <h1>Welcome to this page!</h1>
    <img src="logo.png">
  </body>
</html>

Rather than add these tags in a <head> section within each and every file, we could define a partial, then reuse it throughout the site.

We define the header in partials/header.html:

{{ define "header" }}
  <head>
    <meta charset="UTF-8">
    <meta name="author" content="Gruntwork">
  </head>
{{ end }}

Then we set up the structure in templates/boilerplate.yml:

partials:
  - ../partials/*.html

In templates/page.html:

<html>
{{ template "header" }}
  <body>
    <h1>Welcome to this page!</h1>
    <img src="logo.png">
  </body>
</html>

The contents of the header template will be rendered within page.html and any other page in which we call the header partial.

Let's see a slightly more involved example.

<html>
  <head>
    <title>Welcome!</title>
  </head>
  <body>
    <h1>Welcome to this page!</h1>
    <img src="logo.png">
  </body>
</html>

The example above shows the HTML for a web page, with a title, a welcome message, and a logo. Now, if we wanted to have another page showing a different title and body, we'd have to duplicate all of that content.

In the example below, we'll create a partial that represents the basic layout of the site, then reuse that layout for each page. First, we create a directory structure to keep everything organized:

.
├── partials
│   └── layout.html
└── template
    ├── about
    │   ├── about.html
    │   └── boilerplate.yml
    └── root
        ├── boilerplate.yml
        └── index.html

In partials/layout.html, we create the basic page layout:

{{ define "basic_layout" }}
<html>
  <head>
    <title>{{ .Title }}</title>
  </head>
  <body>
    {{ template "body" . }}
  </body>
</html>
{{ end }}

Now, in each of the pages on the site, we can reuse this layout. For example, from the site's root, we want the welcome page. We create the boilerplate.yml first:

partials:
  - ../../partials/*.html

variables:
  - name: Title
    description: A title for the page.
    default: "Welcome!"

Now we can use the layout within our index.html:

{{- define "body" -}}
    <h1>This is index.html.</h1>
    <img src="logo.png">
{{- end -}}
{{- template "basic_layout" . -}}

When we run boilerplate, basic_layout template will be rendered with the contents of the index.html. Then we can use the same layout for the about page, with its corresponding boilerplate.yml.

Contents of about/boilerplate.yml:

partials:
  - ../../partials/*.html

variables:
  - name: Title
    description: A title for the page.
    default: "About"

about/about.html:

{{- define "body" -}}
    <h1>This is about.html.</h1>
{{- end -}}
{{- template "basic_layout" . -}}

Partials do not need to be located in a magic partials directory. Partials can be located anywhere and referred to using relative paths.

The list of partials is a glob that can match multiple files. The content of all of the files that match the globs will be parsed when rendering the final template. For example, you could match many HTML files at once with:

partials:
  - ../../html/*.html
  - ../../css/*.css

You can use the template definitions from any of the included partials throughout your templates.

You can use Go templating syntax in partial paths. For example, you can define a convenenience variable for a relative path to make the paths slightly easier to read:

variables:
  - name: TemplatesRoot
    description: A convenience variable identify the relative path to the root of the templates directory.
    default: ../../../../
partials:
  - "{{ .TemplatesRoot }}/html/*.html"
  - "{{ .TemplatesRoot }}/css/*.css"

Alternative project generators

Before creating Boilerplate, we tried a number of other project generators, but none of them met all of our requirements. We list these alternatives below as a thank you to the creators of those projects for inspiring many of the ideas in Boilerplate and so you can try out other projects if Boilerplate doesn't work for you:

cookiecutter: Project generator written in Python. Uses Jinja templates, which are reasonably pleasant to work with, and has a huge community. However, the dependency on Python makes cross-platform usage tricky, and the cookiecutter.json file is quite limited in what you can do.
yeoman: Project generator written in JavaScript. Good UI and huge community. However, very focused on generating web projects, and creating new generators is complicated and built around NPM. Not clear if it supports non-interactive mode.
plop: Project generator written in JavaScript. Good UI and templating features. Does not support non-interactive mode.
giter8: Project generator written in Scala. A good option if you're already using the JVM (e.g. you're generating a Scala project), but too long of a startup time (due to all the jars it needs to download) if you're not.
plate: Project generator written in Go. Many of the ideas for boilerplate came from this tool. Does not support non-interactive mode and has not been updated in 2+ years.
generator-yoga: Project generator written in JavaScript. Supports templating for file copy and file contents. Interop with Yeoman. Does not support non-interactive mode.
hugo: Static website generator written in Go. Uses Go templates. Very focused on generating websites, HTML, themes, etc, and doesn't support interactive prompts, so it's not a great fit for other types of project generation.
jekyll: Static website generator written in Ruby. Huge community. Very focused on generating websites, HTML, themes, etc, and doesn't support interactive prompts, so it's not a great fit for other types of project generation.
play-doc: Documentation generator used by the Play Framework that allows code snippets to be loaded from external files. Great for ensuring the code snippets in your docs are from files that are compiled and tested, but does not work as a general-purpose project generator.

License

This code is released under the Mozilla Public License Version 2.0. Please see LICENSE and NOTICE for more details.

Name		Name	Last commit message	Last commit date
Latest commit History 335 Commits
.circleci		.circleci
.github		.github
cli		cli
config		config
docs		docs
errors		errors
examples		examples
getter-helper		getter-helper
integration-tests		integration-tests
options		options
render		render
templates		templates
test-fixtures		test-fixtures
util		util
variables		variables
.gitignore		.gitignore
.gon_amd64.hcl		.gon_amd64.hcl
.gon_arm64.hcl		.gon_arm64.hcl
CODEOWNERS		CODEOWNERS
LICENSE		LICENSE
NOTICE		NOTICE
README.md		README.md
go.mod		go.mod
go.sum		go.sum
main.go		main.go

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Variable Ordering

Alternative Template Engines (EXPERIMENTAL)

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